The present invention relates to a deflection yoke suitable for use in a cathode ray tube, a cathode-ray tube device using the deflection yoke, and a display device which uses such a deflection yoke. In particular, the invention relates to a high-sensitivity deflection yoke which is adaptable for use in a color cathode ray tube with a wide deflection angle and short overall length, as well as to a display device using such a deflection yoke.
"National Technical Report", Vol. 42, No. 3, pp. 93-100 discloses conventional examples of both a color cathode ray tube used for a display device, in which a diagonal dimension of a fluorescent screen is about 410 mm, with a deflection angle of about 100.degree. (hereinafter called "41 cm-100.degree."), and a deflection yoke employed in the color cathode ray tube. The outside diameter of the neck of the conventional color cathode ray tube described in this reference is 29.1 mm (hereinafter called "29.1 mm neck"). The deflection yoke used in this type of color cathode ray tube is commercially available.
The axial length of the color cathode ray tube illustrated in the National Technical Report is 348 mm, and the tube-axial length of the horizontal deflection coil of the deflection yoke used in the color cathode ray tube is long--approximately 93 mm. When the axial length is shortened further, this deflection yoke cannot be used, and new development is needed.
The minimum inside diameter of the horizontal deflection coil in the conventional deflection yoke is large--on the order of 31.5 mm. In the case of a tube-axial position in which the inner surface of a circular deflection yoke has a diameter of 56.5 mm, the length of the portion of the horizontal deflection coil which extends to the opening end of the deflection yoke is about 37 mm, and the length of the portion which extends to the end on the neck side, is about 56 mm. Thus, its overall length reaches 93 mm. Further, such a deflection yoke has the additional drawback that because a fringe is formed on the opening side of the horizontal deflection coil, in a circle having a diameter of about 165 mm, the inductance of the horizontal deflection coil increases due to a magnetic field that does not contribute to the deflection of the opening-side fringe. As a result, horizontal deflecting sensitivity is deteriorated.
It is important that the deflection yoke reduce the undesired emissive magnetic field generated around the cathode-ray tube device, at least to a given value. For example, a guideline called "TCO" addresses the undesired emissive magnetic field in a low frequency band of 400 kHz or less in particular. This guideline stipulates that extremely low frequency magnetic fields (ELMF) of 5 Hz to 2 kHz that leaks principally from a vertical deflection coil of the deflection yoke, should be kept at or below 200 nT (Tesla) at a measurement point 50 cm around the display device and 30 cm from a tube surface of the cathode-ray tube device. Also very low frequency magnetic fields (VLMF) of 2 kHz to 400 kHz that principally leak from the horizontal deflection coil of the deflection yoke, should be maintained at 25 nT or less.
Since the deflection yoke is regarded as the principal generation source of ELMF and VLMF, it has frequently been proposed to provide means for allowing the deflection yoke to generate a reversed polarity magnetic field, thereby reducing the undesired emissive magnetic field to the normalized value or less in order to cancel the undesired emissive magnetic field.
An undesired emissive magnetic field reduction device is disclosed, for example, in Japanese Patent Application Laid-Open No. Hei 3-289029. In this arrangement, respective canceling coils for reducing undesired emissive magnetic fields are electrically connected to a horizontal deflection coil and a vertical deflection coil, which are used to generate additional magnetic fields that cancel the undesired emissive magnetic fields generated from the horizontal deflection coil and the vertical deflection coil. In this manner, the undesired emissive magnetic fields are reduced.
In the above prior art, however, connection of the canceling coils to both the coils causes a reduction or desensitization in horizontal deflecting sensitivity and vertical deflecting sensitivity. Further, the connection of the canceling coils as described above increases the shape of the deflection yoke and increases the cost of the deflection yoke.